1. Field of the Invention
The present invention relates to a connecting device having first and second housing parts, which can rotate relative to one another, and between which there is at least one flexible cable element whose first and second end sections can be rolled up or unrolled in a spiral or helix on associated contact surfaces of the first and second housing parts, respectively, and whose middle section has a U-shaped turning area in which the winding direction is reversed, as well as means to control the unrolling of the cable element when the cable element is rolled up and/or unrolled on the contact surfaces as the two housing parts rotate relative to one another.
2. Background Art
Such a connecting device can be used, for example, in a steering device for motor vehicles. There it serves to transfer electric current (especially signal and/or power current) to the steering wheel from a motor vehicle's on-board electronic system, which is fixedly attached to the body, or vice versa. This makes it possible to integrate into the steering wheel electrical or electronic functional elements that are provided on it, such as, e.g., ignition of the gas generator of an airbag unit, a steering wheel heater, an electric switch to activate blinkers, windshield wipers, or a radio, and to supply them with current from the on-board electronic system. Such a device is disclosed by EP 0 556 779 B1, for example. This device includes an outer housing part, which is associated with a subassembly that is stationary with respect to the rotation of the steering wheel, such as, e.g., the steering column cover of the steering device, as well as an inner housing part that is concentric to the outer housing part and that is associated with the steering wheel and can be rotated together with it. The outer and inner housing parts enclose a ring-shaped cavity, which has arranged in it flexible cables for electrical connection of the outer housing part with the inner one. The end sections of these flexible cables are fastened to the stationary and movable housing parts and, when the two housing parts rotate relative to one another, they can be rolled up or unrolled on their inner or outer peripheral surfaces, respectively. In a middle area, the flexible cables have a U-shaped turning area, in which the winding direction of the flexible cable on the one housing part reverses relative to the other housing part. In particular, EP 0 556 779 B1 proposes arranging several U-shaped turning areas which are distributed around the periphery of the inner or outer housing part spaced at equal angular distances from one another. In the area of a U-shaped turning section the radially further inward or radially further outward end sections of adjacent cables are pressed against the corresponding inner or outer contact surface. Thus, in the arrangement proposed in EP 0 556 779 B1, the cables are fixed against their contact surfaces at regular intervals around the entire periphery. The disadvantage of the known arrangement is that, given the number of four connecting cables that is usually used in steering wheel devices, the support places formed by the four turning areas lie so far apart that a loosening of the cables can still occur in the sections lying between them. This causes collisions and friction of adjacent cables among one another, which not only disturbs the unrolling movement, but rather also exposes the cables to even greater wear.
DE 40 04 233 A1 also discloses a connecting device of the type mentioned at the beginning, in which the cables can be rolled up and unrolled horizontally, in contrast to the vertical cable arrangement from EP 556 779 B1. For example, DE 40 04 233 A1 describes an embodiment in which a flat cable is deformed as a whole so that flat sides of its windings lying on top of one another in layers have the shape of a type of helix or a corkscrew and the same central axis. Thus, the windings have the same outside and inside diameters. In another embodiment, the cable has a spiral shape in which several coaxial windings are radially adjacent in one and the same plane, so that the inside and outside diameters of the windings decrease or increase in the radial direction. In both embodiments the housing parts are formed by an inner cylindrical shaft section and a plate-like top flange extending radially outward from the top end of the shaft section and an outer cylindrical section, which is arranged coaxial to the inner shaft section, and a plate-like bottom flange extending radially outward from its bottom end. The contact surfaces for the cable elements are the surfaces of the horizontal flanges that face one another. Between the two plate-like flanges is the U-shaped turning loop where the direction of winding reverses. In particular, it is possible, analogous to EP 556 779 A1, to provide several cables with several U-shaped turning loops distributed around the periphery which are intended to support the cable layers against one another. According to the publication, even this horizontal arrangement can have the problem that parts of the cable moving in opposite directions rub against one another, which destroys them, which is why the use of spacers is proposed in a preferred embodiment.